Fuel injection system for internalcombustion engines



Sept. 14,1948.

L.. s. GREENLAND FUEL'INJECTION SYSTEM FOR INTERNAL-COMBUSTION ENGINESFiled Dec. 29', 1945 s Sheets-Sheet 1 Sept. 14, 1948. L. s. GREENLAND'2,449,463

FUEL mmcnon SYSTEM FOR INTERNAL-COMBUSTION ENGINES Filed Dec. 29, 1945 I3 Sheets-sheaf? Sept; 14, 1948. L. s. GREENLAND 2,449,468

' FUEL INJECTION SYSTEM FOR INTERNAL-COMBUSTION ENGINES Filed Dec. 29,1945 3 sheets -sheet 3 Patented Sept. 14. 1948 FUEL INJECTION SYSTEM FORINTERNAL- COMBU STION ENGINES Leonard Sidney Greenland,Weston-super-Mare, England, assignor to H. M. Hobson Limited, London,England, a company of Great Britain Application December 29,1945,"Serial No.

i In Great Britain February 12, 1945 4 Claims. (Cl. 123-119) Thisinvention relates to fuel injection systems for internal combustionengines of the type in which fuel is fed under pressure by an enginedriven fuel pump to a metering unit, comprising a variable area fuelmetering orifice, means for varying the area of said orifice as adesired function of boost pressure and preferably also of exhaust backpressure and induction temperature,

' and means controlled by a centrifugal impeller coupledto the pump forestablishing across the metering orifice a metering pressure which issome fraction of the pressure difference developed by the impeller. Ininjection systems of this type, as is well known, the metering pressureis substantially proportional to the square of the.

engine speed and the now of fuel through the orifice varies as asubstantially linear function of engine speed.

It has hitherto been the practice to construct the fuel pump andimpeller as a single unit-separate from the metering unit and connectedthereto by pipes for carrying the main fuel supply and transmitting themetering pressure. This is disadvantageous for the fol owing reason. The

pressure difference generated across the impeller According to theinvention the fuel pump and iil'ipeller are built into the metering unitand a readily detachable coupling is provided between the fuel pump andthe impeller. so that the pump can be removed, if required, withoutdisturbing the impeller. This arrangement has two advantages. Firstlythe connections for applying the metering pressure from the impeller tothe orifice can be constituted by short drilled passages in the housingof the metering unit, which will reduce pressure losses to a minimum anddispense with the many variables inherentin the use of pipes. Anotheradvantage is that once the impeller is 'built into the metering unit, itremains with the unit, and when the fuel pump is changed the fuelmetering system is not interfered with in any way. Thus a pump couldbechanged on an engine in service without any fear ofthe fuel flowcharacteristics being altered in any way. In

' however, if the pump is changed the-impeller is the case of a separatepump and impellerunit,

changed with it and the accuracy of the metering system with the newpump will depend upon the similarity of the two metering impellers.

In service it is much more usual for a fuel pump 4 to failthan for thefuel metering unit to fail. Apart from the impeller, there are no partsin the injection system subjected to high speed movement and theimpeller itself is not likely to be subjected to wear; on the otherhand, a fuel pump unit with its gears or vanes and glands,-

is subjected to wear and has to be removed more frequently than themetering unit. a It is also subject to mechanical breakdown due toforeign matter entering the pumping unit.

One specific form of fuel injector for aircraft engines according to theinvention will now be described in detail, by way of example, withreference to the accompanying drawings, in which:

Fig. 11s a diagram illustrating the operation of the injector,

Fig. 2 is an exploded perspective'view of the injector, and

Fig. 3 is a horizontal section, through the in- :Iector.

Like reference characters designate like parts throughout the figures.

The general operation of the injector will first be described withreference to Fig. 1, and the specific construction of those parts of theapparatus which are concerned with the ready removal and interchange ofthe fuel pump will thereafter be described with reference to Figs. 2 and3.

The apparatus shown in Fig. 1 is fully described in my copending U. S.application Serial No. 638,128. filed December 29, 1945, and now PatentNo. 2.438,631, and it will be suflicient here to explain that fuel ispumped from an inlet ill by an engine-driven gear wheel pump H to a highpressure chamber 12 and thence through a I 6, linked by a bell cranklever ll, pivoted at It.

to a pressure regulating valve I9. The fuel leaves chamber. Ii via thepressure regulating valve and passes on through a pipe 20 and past abalanced discharge valve 2 i to a discharge nozzle 2?! through which itis injected into the induction pipe 23.

The pressure difference across the meterin orifice i3 is maintainedsubstantially proportional to the square of engine speed by utilisingthe difference of pressure generated across a centrifugal impeller 24coupled to the pump i I by a dog clutch 25 and deriving movement fromthe engine by 3 means of a shaft 26. The pressure at the tip of theimpeller 24 is applied via a conduit 21 to the entry side of themetering orifice and the pressure at the eye of the impeller is appliedby a conduit 28 to chamber I4. The diaphragm I6 and pressure regulatingvalve I9 therefore operate, as described in U. S. Patent No. 2,374,844,to maintain across the metering orifice I3 some fraction of the pressuredifference developed by the impeller 24. 29 is a vent orifice forallowing air or vapour which may collect at the eye of the impeller tovent forward to the downstream side of the metering orifice I3. Abiasing spring 30, operating on the diaphragm I6 serves to enrich themixture at slow running as described in my copending U. S. applicationSerial No. 638,128, filed December 29, 1945. Adjustment for initialtuning is provided by an orifice 3| adjustable by a screw 32, throughwhich a small quantity of fuel can by-pa-ss the metering orifice.

The effective area of the metering orifice I3 is controlled by a needlevalve 33, which is varied in position as a Joint function of boostpressure, exhaust back pressure and induction temperature. The first twocorrections in the area of the metering orifice are provided by a pairof balanced capsules 34, 35 located in the fuel chamber I2. Capsule 34is exposed internally to boost pressure, being connected to theinduction pipe '23 by a pipe 36. The greater part of capsule isevacuated, but the rear section thereof 31 communicates with the exhaustpipe 38 via conduit 39. To a trunnion 40 on a rod 4I connecting the freeends of the two capsules is pivoted a a forked lever 42, pivoted at 43to the stem of the needle valve 33, and at 44 to a Bourdon tube assembly45 which adjusts the position of the pivot 44 to conform withalterations in induction temperature under the control of a thermometerbulb 46. Capsules 34, 35 are anchored at their outer ends to the wallsof chamber I2. Axial movement of rod 4| in response to expansion orcontraction of the capsules, effects an appropriate change in theposition of needle valve 33 by causing lever 42 to rock about pivot 44.On change in induction temperature, lever 42 adjusts needle valve 33 byrocking about trunnion 40.

41 is a lever, coupled to the pilot's throttle lever, and arranged, whenmoved rapidly in the direction to accelerate the engine (1. e.anticlockwise between the sloW running position S. R. and the fullthrottle position F. T.) to operate through link 48 an accelerator pump49, so as temporarily to supply extra fuel to the engine through pipe50. Link 48 is coupled to a bell crank I48. and as lever 41 is movedtowards the full throttle position, a piston I49 is moved by bell crankI49 to the right. The resultant fall of pressure to the right ofdiaphragm I50 causes the latter to be displaced to the right, opening avalve I5I and allowing a temporary additional supply of fuel to flow tothe pipe 20 via pipe 50. The diaphragm I50 slowly returns under theaction of spring I52, displacing fuel from its left to its right handside via a restricted orifice I53. A restriction I54 regulates thequantity of fuel supplied to the pump 49 during acceleration. Anon-return valve I55 permits of unobstructed movement of piston I49 tothe left when the lever 41 is moved to decelerate. When the lever 41 ismoved clockwise beyond the S. R. position, it closes a cut-off valve 52which is normally held open by a spring 5I.

The pump II is provided with a diaphragm engine is stationary.

operated relief valve 52 for returning excess fuel valve, through whichfuel can be supplied to the engine by a. priming pump at times when the56 is a normally closed the capsules and is formed with an aperture 92by which atmospheric pressure-which in this instance is taken as ameasure of exhaust back pressure-is applied to the interior of capsule31. To the front of housing 51 is fitted a fuel pump body 63, which fitsover threaded studs 94 on the 7 housing 51, and is held in position bynuts (not shown) fitted to said studs. A fuel pump assembly fits insidethe body 33 being located in position by a cover plate 66 and bolts '81which pass through holes 88 in the assembly 33 and are screwed intotapped holes 69 in the body 83. The

whole is covered by a screwed ring 19 which screws over threads II onthe body 33.

The gear pump has two gear wheels I2, I3

mounted on spindles 14, II respectively. When the parts are assembled,as shown in Fig. 3, spindle 14 engages via dog clutch 25 with the driveshaft 26 carrying the impeller 24, and spindle I5 abuts via a washer I6,with the priming valve 55. A spring 11 is provided adjacentthe dogclutch, and the shaft 29 carries a pinion I8 by which it derives motionfrom the engine. Spring 11 urges shaft 28 to the right as seen in Fig.3, to maintain a bearing member I9 adjacent the impeller 24 pressedagainst a carbon disc 89. Spring I1 thus prevents the shaft 29 frommoving to the left suificiently for the lefthand face of the impeller tofoul the right-hand face of the pump body 63. Spring ll forms part of aseal for preventing leakage of fuel along the shaft 26. Spring 8Ipresses a sealing housing 22 against a carbon ring 83 anda bearingmember 84 against a carbon ring 85. A sealing element- 33 is disposedbetween the housing 92 and the shaft 28.

It will be apparent that the pump II can readily be removed and changedwithout disturbing the impeller 24, by unscrewing the cap I0 andremoving the cover plate 66. If the gear wheels only are damaged, theassembly 95 and gear wheels are removed and replaced, but if the damageto the pump is .more extensive the pump body 63 is also removed. Ineither case the impeller 24 is undisturbed, and the new pump is at oncecoupled to the impeller by means of the dog clutch. The weakest sectionof the drive shaftis arranged to be at the location I14 on the pumpdriving spindle 14 on the pump side of the dog clutch 25 so that in theevent of the gear pump seizing up, the shaft will break at I" in thegear pump, and the drive shaft 26 running through the metering unit andcarrying the impeller 24 will not be damaged.

During priming of the engine, fuel is pumped by a priming pump into theinlet I9 and passes thence through the hollow spindle II and the thenopen priming naive to the chamber l2 and thence to the engine.

What I claim as my invention and desire to segine driven fuel pump, anenginedriven' cen-.

trifugal impeller; a. metering unit, and means for supplying fuel fromthe fuel pump to the metering unit, said metering unit comprising,within an enclosing housing. a variable area fuel metering orifice,means for varying the area of said orifice as a desired" function ofboost pressure and means controlled by said impeller forestablishingacross the meteringorifice a metering pressure which is some fraction ofthe pressure diiference developed by said impeller, characterised inthat said fuelpump and impeller are built into the housing of themetering unit and in that a readily detachable drive connection isprovided between said pump and said impeller which permits of removal ofsaid pump from said housing without disturbing said impeller and themeans controlled thereby for establishing said metering pressure.

2. A metering unit for use in a fuel injection system for an intemaicombustion engine, said unit comprising, within an enclosing housing, afuel pump, a centrifugal impeller, a clutch connecting said pump andsaid impeller, a variable area fuel metering orifice. a conduit forsupplying fuel from the pump to the metering orifice and thence to anoutlet, means for varying the area of said oriflceas a desired functionof boost pressure, mean for maintaining across said oriflce a meteringpressure which is some'fraction of the pressure diflerence developed bysaid impeller, and a shaft for. driving the impeller, which shaftprojects from said'housing and is adapted to be driven by the engine, aremovable cover plate being fitted to saidhousing, which plate, whenremoved,'perrnits of withdrawal of said pump from thehousing bydisengagement of the clutch and without disturbing theimpellere 3. Ametering unit as claimed in mama, in

"which the pump has a drivespindlefor trans-.

drive spindle being weaker than the impeller mitting the drivtheretofrom the clutch, said drive shaft, "so that it will break inpreference to the impeller driv seizure.

4. A metering unit as claimed in claim 2,5111 1 which the fuel pump isagear wheel pumpand the clutch is a dog clutch. a

LEONARD SIDNEY GREENLAND.

REFERENCES cITnn The following references are of record in the file ofthis patent:

UNITED STATES PATENTS England v July 25, 1940 shaft in the eventof pump;

